The invention relates to a charging control system for a battery of rechargeable electric storage cells and more particularly for a battery made up of lithium cells.
The cells of rechargeable lithium batteries of the lithium-ion and lithium-metal type offer significantly better performance in terms of energy and mass than rechargeable nickel-cadmium or nickel-hydrogen cells. However, they are not totally satisfactory in applications where long life and high reliability are required, in particular with regard to controlling their charge in ampere-hours while they are in use.
A lithium cell is less able to withstand temporary or permanent overcharging than a nickel-cadmium or nickel-hydride cell, in which overcharging does not cause any perceptible deterioration. In the case of a lithium-carbon cell, overcharging forms a deposit of carbonate which cannot afterwards recombine with the active material of the cell. Active material is therefore consumed each time the cell is overcharged, which represents an irreversible loss of cell capacity. It is therefore beneficial to control batteries made up of lithium cells in an appropriate manner that takes this characteristic into account.
For practical and economic reasons, the charging of a battery is usually controlled by a central control unit which controls the charging current supplied to all of the cells constituting the battery and in particular how the charging current is reduced at the end of charging. Individual auxiliary control units allocated to the cells provide accurate control of the end of charging on a cell by cell basis.
The present invention therefore proposes a charging system for a battery of electric storage cells, and more particularly for a battery made up of lithium cells, the system being intended to optimize control of the cells, and in particular to prevent a reduction in their capacity over time.
The charging control system is therefore intended to be associated with a battery of rechargeable electric storage cells including a plurality of cells connected in series and each of which is associated with means adapted to be connected to a common electrical power supply and to take therefrom the energy necessary for charging the cell with which they are associated.
According to a feature of the invention, the system includes individual cell charging control units each including the means for taking the energy necessary for charging one of the cells from the common supply, to which said means are connected, and means enabling the unit itself to provide all of the charging operations for said cell using the energy supplied by its means for taking energy.
According to the invention, a power supply bus connects the connecting systems of each of the individual control units to the connecting system of the supply.
According to the invention, each cell charging control unit includes means for supplying the current necessary for charging the cell from the energy that the unit takes from the supply, which current depends on the voltage at the terminals of the cell and is kept below a value that corresponds to a predetermined fraction of the capacity of the cell.
The invention also proposes a battery of rechargeable electric storage cells comprising a plurality of cells connected in series and each of which is associated with means adapted to be connected to a common electrical power supply and to take the energy necessary for charging the associated cell.
According to a feature of the invention, the battery includes a charging control system including a set of individual cell charging control units each including means for taking the energy necessary for charging one of the cells from the common supply, to which said means are connected, and means enabling the unit itself to provide all of the charging operations for said cell from the energy provided by its means for taking energy.
According to the invention, the individual cell charging control units and the cells are combined into modules each including one cell and one charging control unit by which the cell is individually powered from a common bus connected to the supply and via supply connecting systems and module connecting systems.